1. Field of the Invention
The present invention relates to a micro mirror, and in particular, to a micro mirror capable of being used as an optical scanner for scanning laser beams in a display device such as a laser TV, and a method for fabricating the same.
2. Description of the Related Art
As the age of multimedia has arrived, demand for large-display is increased and various types of large-display devices are successively introduced. A laser TV is proposed as a display device for next generation that can implement high-resolution at a low price and large size.
Such a laser TV includes an optical scanner that scans laser beams projected from a laser diode module in horizontal and vertical directions according to RGB image signals. The optical scanner includes a micro mirror fabricated on the basis of Micro-Electro Mechanical System (MEMS).
FIGS. 1A and 1B schematically illustrate different types of micro mirrors publicly known in the prior art, and FIG. 2 is a drawing for describing the operations of these micro mirrors.
As can be seen from the drawings, a micro mirror comprises a rotatable mirror section 1, a pair of spring sections 2 and 2′ connected to the mirror section 1 to support the mirror section 1 and to serve as a rotation axis when the mirror section 1 rotates, a mobile comb 3, and a fixed comb 4.
The mobile comb 3 and the fixed comb 4 have a plurality of comb-fingers 3a, 3b, . . . ; 4a, 4b, . . . , respectively. The mobile comb 3 may be installed either on the mirror section 1 as shown in FIG. 1A or on the spring sections 2 and 2′ as shown in FIG. 1B. The fixed comb 4 may be installed above or below the mobile comb 3, as shown in FIG. 2, wherein they are arranged in such a manner that the comb-fingers 3a, 3b, . . . of the mobile comb 3 and the comb-fingers 4a, 4b, . . . of the fixed comb 4 are clasped each other.
Therefore, if plus (+) voltage is applied to one side comb-fingers 4a among the comb-fingers 4a, 4b of the fixed comb 4 corresponding to the comb-fingers 3a, 3b of the mobile comb 3 electrified to minus (−), electrostatic force is generated between the comb-fingers 3a and 4a, and accordingly, the mirror section 1 is rotationally driven about the spring sections 2 and 2′, as indicated by dotted lines in FIG. 2. Whereas, if plus (+) voltage is applied to the other side comb-fingers 4b, the mirror section 1 is rotationally driven in the reverse direction. Due to this rotational driving of the mirror section 1, incident light is scanned to a scanning surface while being continuously and uniformly reflected to a predetermined angle range.
The driving velocity of the micro mirror is related to resolution of a display device, and the driving angle is related to a picture screen size of such a display device. That is, as the driving velocity of the micro mirror is increased, the resolution is also increased, and as the driving angle is increased, the picture screen is also increased. Therefore, in order to implement a large high-resolution laser TV, an optical scanner such as a micro mirror is required which has an increased driving angle while being driven in high velocity.
However, since driving velocity and driving angle of a micro mirror conflict each other, there is difficulty in increasing driving angle of a micro mirror and the driving velocity thereof at the same time. Resonance driving may be used in order to increase a driving angle of a micro mirror. However, this has a problem in that the yield of production is very low since it is very difficult to match the natural frequency of a micro mirror with a driving frequency due to an error in fabrication, and thus a tuning structure is required for tuning the driving frequency.
In a conventional micro mirror as shown in FIG. 1A, the mobile comb 3 is arranged on the opposite sides of a mirror section 1, in which case since a distance D1 from the rotational center of the mirror section 1 is long, a moment is increased as compared to the case in which the comb fingers of the mobile combs 3 are arranged on the spring sections 2 and 2′ as shown in FIG. 1B, if the same number of comb-fingers are employed. However, in this case, the number of mobile comb 3 is limited, and in addition, the size of mirror section 1 is increased in order to provide an increased number of comb-fingers of mobile comb 3, the inertia moment will be increased, and thus the natural frequency of the mirror will be lowered. Accordingly, driving velocity can not be increased.
Meanwhile, in a micro mirror as shown in FIG. 1B, the mobile combs 3 are arranged on spring sections 2 and 2′, in which case it is possible to reduce the magnitude of rotational inertia moment while increasing the number of mobile combs 3, as compared to the mirror having the structure shown in FIG. 1A. However, it is impossible to obtain a sufficient driving angle since the distance D2 from the central axis of the mirror section is short, thereby generating low moment. In addition, this case has a problem in that the rigidity of the spring sections 2 and 2′ is not uniform due to a process error or the like.
Thus, the conventional micro mirrors as described above is hard to satisfy high driving velocity and an increased driving angle due to their constructions. Therefore, the conventional micro mirrors are not suitable for an optical scanner for a large high-resolution laser TV.